In the commercial environment of perishable food products, the refrigeration or cooling cabinets are well known, especially the ones having transparent front doors allowing products in the interior to be seen. However, it is necessary to have a lighting system in the interior of the cabinet in order to improve the display of items.
Nowadays, fluorescence lamps are used which are mounted on the door or at the inner side of the cabinet in a vertical manner or at the top of the cabinet in a horizontal manner in order to light the item to be displayed. An example of said system is described in the U.S. Pat. No. 5,937,666 (Trulaske, Sr., 1999), where a lighting system comprised by fluorescence lamps is disposed adjacent to the frame spar of the doors, in the interior side, being hidden from view from the exterior side; a support base is used and having open ends and running along said spar, two connecting elements for the lighting element located at the ends and including in some embodiments, a diffuser surrounding the fluorescent tube. Being the lamp vertically mounted on the door or laterally mounted on the side of the cabinet, the item located at the front up to the middle part is lightened so the rest of the items remain unlighted. Another example of a similar application is described in the U.S. Pat. No. 6,406,108 (Upton et al, 2002), which also uses fluorescent light tubes enclosed in a channel designed so in turn it is located in the door frame of the refrigeration cabinet.
In the lighting systems available nowadays, bigger lateral luminaries are placed in one or both sides of the interior of the cooler. Also, luminaries are disposed vertically on the door in order to light most of the item. Additional fluorescence lamps may be used in order to best display the item, holding horizontal lamps along the crossing sections of the door frames. However, by doing this, the power consumption increases since there are more luminaries, and so the heat issued increases as well, and a very short lifetime of the fluorescent luminary is maintained as well as the light drop due to low temperatures at the interior of the cooler. Likewise, high costs for services due to failures in the lighting system are maintained. Besides, when the fluorescence lamp is found at the top side of the cabinet, there is the problem that only the acrylic display and the first grid of the item is being lightened, and thus the remaining grids and the remaining items located at the middle part and up to the bottom part remain unlighted and unseen properly.
An important problem related to lighting an item is high costs of maintenance of equipments due to failures in the components of the lighting systems. A fluorescent luminary has a lifetime of about 9,000-13,000 hrs, this means 1 year or a bit more, pursuant to which the luminary or ballast are commonly replaced every year and costs for service are quite high. Moreover, fluorescent luminaries are very sensitive to room temperature. The light peak is reached in a fluorescent luminary at 30° C. but it quickly drops when temperature ranges on both sides, whether at high or low temperature. With low temperatures, fluorescence lamps have a light drop of 20% operating at a temperature of 7° C. and if temperatures are lower then it will drop even more. In addition, due to the configuration of the fluorescence lamps, only 60% of the light is used to light the cabinet, the rest goes outside the cabinet. Fluorescence lamps contribute to add heat obtained inside the cooler, thus diminishing the efficiency of the cooling system. Less of 25% of the total power consumed by a fluorescence lamp is turned into light, the remaining power is turned into heat. More than a half of the radiated heat-type heat is absorbed by the item located at the interior of the cooler. In addition, heat generated by fluorescent luminaries contributes to the uneven distribution of temperatures at the interior of the cabinet. (“Solid-State Lighting for refrigerated Display cases”, pages 64-67, New technologies in Commercial Refrigeration, University of Illinois at Urbana-Champaign, P. S. Hrnjak Editor, Jul. 22 and 23, 2002).
In order to overcome problems pertinent to the use of fluorescence lamps, it was suggested to replace this lighting source for sets of LED lights (light emitting diodes), as illustrated, for example, in the U.S. Pat. No. 6,726,341 (Pashley et al, 2004) which describes a storage compartment equipped with a lighting source based on LEDs positioned so preferably the interior of the cabinet is lightened; the U.S. Pat. No. 7,121,675 (Ter-Hovhannisaian, 2006) describes, in turn, a lighting system for environments of low temperature including a plurality of light emitting diodes subject to a support member mounted inside a refrigeration unit, the system includes a reflector close to the LEDs in order to spread emitted light, like a light transmitting cover which covers the LEDs, where said cover includes non-planar surfaces to spread light over the items at the interior of the cabinet. The system is intended to be mounted on the spar of the door frame or otherwise, preferably, on the inner trays of the cabinet, so lighting of items is optimized.
In this last patent, arrangements of LEDs mounted on the support members are described so arrangements over a circuit board are formed and sealed. Arrangements are linear and the reflector is distributed along said linear arrangements of LEDs. Arrangements may be constructed of any length or configuration required for a particular application, they are preferred to be embodied in multiple lighting units electrically interconnected with each other, being said lighting units of a length of only 90 cm, and if interconnection can be achieved by means of a wiring, the use of caps including electrical connectors subject to the ends of each unit is desirable, connectors being female and male connectors. Lighting units, even though they are found interconnected, maintain an independent operation so if one of the units is not operable due to failures, it does not alter the operation of the other units
The U.S. Pat. No. 6,283,612 (Hunter, 2001) describes a strip of LEDs that is kept in the interior of a tube that seems to be a fluorescence lamp; the tube contains a printed circuit board with a positive bus and one negative bus extending along the entire card; resistors are included in contact with the positive bus in one end and a set of LEDs on the other end, LEDs are mounted through holes in the card and the anode of the diode is in communication with a resistor whilst the cathode of the diode gets into contact with the anode of diode adjacent connecting each other in shorts sets at the base of the circuit. The final cathode of each set is coupled to the negative bus forming a predetermined group of diodes electrically coupled to a single resistor in one end and the negative bus in the other end. The assembly in the tube is enclosed by two caps at the ends and an electric wire is connected through the caps to the buses of the printed circuit. A power source gets in contact, by means of the wire, with the circuit, providing low voltage direct current to a predetermined group of LEDs in order to light the area surrounding said strip.
By using the tube of LEDs similar to the fluorescent tube is possible then to have a luminary with long lifetime but the problem of uniform lighting is not solved in the entire item to be displayed. For example, the U.S. Pat. No. 6,550,269 (Rudick, 2003) describes a lighting system for the interior of refrigeration cabinets and dispensing products, such as vending machines, coolers, etc., based on directional LEDs positioned so they can light the best possible way the items located closer to the lighting source, that is, those in the front of the cabinet, towards the glass door/window. The directivity of LEDs used is about 20° with a lighting intensity from 5 to 6 candles and a brightness of 1000 to 3000 lumens. Directional LEDs are located over trays, at the door frame and/or in mounting blocks, and may be intended for specific parts of the product, being adjustable. In one example of the invention, it is mentioned the LEDs may be grouped with the shape of a tube, with a diameter of 19 to 32 mm and a length between 30 and 90 cm; each group may contain between 18 and 54 LEDs. However, the invention emphasizes the direction of the lighting with the purpose of stressing specific sections of the product; the lighting of the interior of the cabinet is completed by the use of alternate light sources.
In this sense, some efforts have been focused on the distribution of light emitted from the source selected. Some examples regarding this issue are as follows:
The U.S. Pat. No. 5,471,372 (Mamelson et al, 1995) described a lighting system for a refrigeration cabinet lighted by fluorescence lamp located closer and behind the glass of the doors. Each lamp has a reflector associated and located enclosed at least partially by plastic lens having multiple facets at the interior face. The reflector and the lens cause the light emitted by the lamp is reflected and refracted such that the light is substantially uniform-distributed over the products located at several distances from the lamp and reduce the reflection of the immediate proximity of the lamp.
The U.S. Pat. No. 6,578,979 (Truttmann-Battig, 2003) on the other hand, describes a lighting system based on LEDs comprised in modules consisting of a plastic receptacle with a ground plate where there are carrying networks defining sloped surfaces over which strips of printed circuit with LEDs are placed. LEDs have a projection angle (β) and where this angle corresponds preferably to the tilt angle between the sets of LEDs (α), in this way the radiation angles of several parallel arrangements of LEDs cover a wider area of a single strip. The set of LEDs thus comprised is fixed to the interior of the plastic receptacle having a section in “U”, and the open face is covered by a transparent and curved sheet; in this way the lighting angle achieved with the arrangement is best used, being limited, however, by the walls of the plastic receptacle towards the forward direction.
In light of the limitations and problems at the developments thus far suggested in the prior art, it is an object of this invention, to provide an efficient system of lighting for commercial refrigerators and coolers with glass doors, allowing proper lighting and therefore displaying products at the interior of the cabinet.
It is another object of this invention to provide a lighting system for the interior of low maintenance cost cabinets.
It is another object of this invention to provide a lighting system for the interior of the cabinets with an improved diffusion of light emitted regarding known systems, so this allows a uniform lighting of items at the interior of the cabinet.
It is still another object of this invention to provide a lighting system for the interior of the cabinets where the lighting system provides a lighting angle wider than the one of conventional systems.
These and other objects and advantages of this invention will be apparent in light of the description below, which is attached with a set of figures for preferred embodiments of the invention and it will be understood that they are made for illustrative and not limitative purposes of the teachings of the invention.